U.S. patent number 5,410,484 [Application Number 07/893,743] was granted by the patent office on 1995-04-25 for automatic brake control system.
This patent grant is currently assigned to Akebono Brake Industry Co., Ltd., Akebono Research and Development Centre, Ltd.. Invention is credited to Takashi Kunimi, Katsuya Miyake, Kimio Takahashi.
United States Patent |
5,410,484 |
Kunimi , et al. |
April 25, 1995 |
Automatic brake control system
Abstract
In a vehicular automatic brake system, a distance X between a
vehicle to be controlled and an obstacle is determined using a
distance sensor, a relative velocity Vs with respect to the
obstacle is determined from changes of X with time, a judgment is
made as to whether the vehicle to be controlled is approaching the
obstacle, further, an estimated time Tx which will be taken until
contact with the obstacle is determined from Vs and X, and braking
is performed in accordance with the value of Tx.
Inventors: |
Kunimi; Takashi (Tokyo,
JP), Takahashi; Kimio (Kasukabe, JP),
Miyake; Katsuya (Konosu, JP) |
Assignee: |
Akebono Brake Industry Co.,
Ltd. (Tokyo, JP)
Akebono Research and Development Centre, Ltd. (Saitama,
JP)
|
Family
ID: |
26381826 |
Appl.
No.: |
07/893,743 |
Filed: |
June 5, 1992 |
Foreign Application Priority Data
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Jun 5, 1991 [JP] |
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3-042169 U |
Jun 19, 1991 [JP] |
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3-147633 |
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Current U.S.
Class: |
701/70; 180/170;
701/96 |
Current CPC
Class: |
B60T
7/22 (20130101); B60T 8/489 (20130101); B60T
13/662 (20130101) |
Current International
Class: |
B60T
13/66 (20060101); B60T 8/48 (20060101); B60T
7/22 (20060101); B60T 008/32 () |
Field of
Search: |
;364/426.01,426.04,424.05 ;180/169,170 ;340/904 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Teska; Kevin J.
Assistant Examiner: Walder, Jr.; Stephen J.
Attorney, Agent or Firm: Knobbe, Martens, Olson &
Bear
Claims
What is claimed is:
1. An automatic brake control system comprising:
a distance sensor for detecting the distance between a front
obstacle and a vehicle to be controlled:
a brake pressure controller for controlling the application of
pressure, holding of pressure and reduction of pressure for a
hydraulic brake fluid in a wheel cylinder of said vehicle; and
a control section which inputs a signal from said distance sensor,
performs an arithmetic processing and outputs a control signal to
said brake pressure controller,
said control section calculating a distance X between said vehicle
and said obstacle on the basis of the signal provided from said
distance sensor, calculating a relative velocity Vs with respect to
said obstacle from changes of X with time, determining an estimated
time Tx which will be taken until contact with said obstacle, from
both Vs and X, and outputting a control signal for the execution of
braking in accordance with the value of the estimated time Tx;
said control section storing reference times T.sub.0 and T.sub.1
(T.sub.0 >T.sub.1), actuating said brake pressure controller to
pressurize the wheel cylinder for applying the brake when said
estimated time Tx is smaller than both reference times T.sub.0 and
T.sub.1, and calling a driver's attention by blinking a lamp or
issuing a warning sound when said estimated time Tx is smaller than
the reference time T.sub.0 and larger than the reference time
T.sub.1 ;
said control section pre-pressurizing the wheel cylinder to create
a light drag state of the brake when said estimated time Tx is
smaller than the reference time T.sub.0 and larger than the
reference time T.sub.1.
2. An automatic brake control system according to claim 1, wherein
said control section calculates a relative acceleration V's
together with the relative velocity Vs, further calculates a
relative velocity Vs.sub.2 at an elapsed time point of the
estimated time Tx as a rear-end collision estimated time when the
value of the relative acceleration V's is positive, and actuates
said brake pressure controller to pressurize the wheel cylinder for
applying the brake when the value of the relative velocity Vs.sub.2
is positive.
3. An automatic brake control system according to claim 1, wherein
said control section outputs a stop lamp actuating signal at the
time of outputting the control signal to said brake pressure
controller so that a stop lamp in the rear of said vehicle is
activated by either depression of a brake pedal or said stop lamp
actuating signal.
4. An automatic brake control system according to claim 1, wherein
when the estimated time Tx is smaller than the reference time
T.sub.0 and larger than the reference time T.sub.1, a judgment is
made as to whether a brake pedal is depressed or a steering
operation is performed to a predetermined degree, and the braking
is released when either of said operations is performed.
5. An automatic brake control system including:
a distance sensor for detecting the distance between a front
obstacle and a vehicle to be controlled;
a brake pressure controller for controlling the application of
pressure, holding of pressure and reduction of pressure for a
hydraulic brake fluid in a wheel cylinder; and
a control section which inputs a signal from said distance sensor,
performs an arithmetic processing and outputs a control signal to
said brake pressure controller;
said control section holds two reference times T.sub.0 and T.sub.1
(T.sub.0 >T.sub.1), and calculating a distance X between the
vehicle to be controlled and the obstacle on the basis of the
signal provided from said distance sensor, then calculating a
relative victory V.sub.s with respect to the obstacle from changes
of X with time, determining an estimated time T.sub.x which will be
taken until contact with the obstacle, from both V.sub.s and X, and
actuates said brake pressure controller to pressurize the wheel
cylinder for applying the brake when the estimated time T.sub.x is
smaller than both reference times T.sub.0 and T.sub.1, and
pre-pressurizes the wheel cylinder to create a light drag state of
the brake when the estimated time T.sub.x is smaller than the
reference time T.sub.0 and larger than the reference time
T.sub.1.
6. An automatic brake control system according to claim 5, wherein
said control section calls a driver's attention by blinking of a
lamp or by issuing a warning when the estimated time T.sub.x is
smaller than the reference time T.sub.0 and larger than the
reference time T.sub.1.
7. An automatic brake control system according to claim 5, wherein
said control section outputs a stop lamp actuating signal at the
time of outputting the control signal to said brake pressure
controller.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an automatic brake control system
for controlling the running speed of a vehicle automatically.
As this type of an automatic brake control system there is known
the system described in Japanese Patent Laid Open No. 71727/87.
In such automatic brake control system, the distance between a
front obstacle such as a vehicle and a vehicle to be controlled is
detected and the vehicle to be controlled is braked on the basis of
the result of the detection. In the case where the distance from
the obstacle is judged to be sufficient for safe running on the
basis of the result of comparison between a reference running speed
which is determined from a vehicular running speed at the start
point of the braking and a vehicular running speed during the above
braking operation, the braking is released.
In such prior art, however, in many cases there occurs discrepancy
between the braking action and the actual driving sense.
More particularly, in a conventional automatic braking system,
braking is not performed as long as the distance up to a front
vehicle does not reach a predetermined distance, on the basis of
only the running speed of a vehicle to be controlled (hereinafter
referred to as "this vehicle"), irrespective of whether the running
speed of the front vehicle is high or low, if only the running
speed of this vehicle is constant.
Consequently, in the case where the running speed of the front
vehicle is sufficiently high and the front vehicle and this vehicle
are in a relation such that the distance between both vehicles
becomes smaller gradually, braking is performed with a sufficient
time margin, but when the front vehicle is braked suddenly or is at
a standstill, there is little time margin, thus causing a danger of
rear-end collision.
Conversely, if a braking start distance is determined, premising
sudden braking or stopping of the front vehicle, the braking will
be started in a too early stage, causing a danger against a
succeeding vehicle rather than this vehicle, even when vehicles are
running smoothly and the running speed of the preceding vehicle is
sufficiently high.
The present invention has been accomplished in view of the
above-mentioned problem and it is the object of the invention to
provide a technique which permits a braking operation to be
performed in a state closer to the actual driving sense in an
automatic brake control system.
SUMMARY OF THE INVENTION
According to the present invention, in an automatic brake control
system including a distance sensor for detecting the distance
between a front vehicle and this vehicle, a brake pressure
controller, and a control section which inputs a signal from the
distance sensor, performs an arithmetic processing and outputs a
control signal to the brake pressure controller, first a distance X
between this vehicle and an obstacle is determined, then a relative
velocity Vs with respect to the obstacle is determined from changes
in the distance X with the lapse of time, a judgment is made as to
whether this vehicle is approaching the obstacle, further, an
estimated time Tx which will be taken till contact with the
obstacle is determined from both Vs and X, and braking is performed
on the basis of the value of Tx.
According to the present invention, since the estimated time Tx up
to contact with a front vehicle is calculated and braking is
performed in accordance with the value obtained, braking is applied
irrespective of the distance between the front vehicle and this
vehicle if the running speed of the front vehicle is low even when
the running speed of this vehicle is constant, while if the running
speed of the front vehicle is high, braking is applied in a stage
in which the vehicle-to-vehicle distance has become shorter. In
this way, a braking operation is performed in a state extremely
close to the actual driving sense.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart showing an automatic brake control according
to an embodiment of the present invention;
FIG. 2 is a graph showing a fluid quantity-fluid pressure
characteristic for the explanation of pre-pressurizing in FIG.
1;
FIG. 3 is a block diagram of an automatic brake control system
according to the embodiment of the invention; and
FIG. 4 is a flowchart showing an automatic brake control according
to another embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
An embodiment of the present invention will be described below with
reference to FIGS. 1 to 3.
FIG. 3 is a block diagram of an automatic brake control system
according to an embodiment of the present invention.
In this embodiment, upon depression of a brake pedal 1, a master
cylinder 3 sends a hydraulic brake fluid to a pressure accumulating
device 5 and further to a wheel cylinder 9 through a passage 29
formed in a piston 11 which is provided within the pressure
accumulating device 5, allowing the fluid to exhibit a braking
force and effect an actual braking operation.
The piston 11 disposed within the pressure accumulating device 5 is
normally urged rightwards in the figure by means of a spring
13.
A port 15 is formed on the right-hand side of the piston 11 in the
figure, and when a control fluid, e.g. air, which will be described
later is fed into the pressure accumulating device through the port
15, the piston 11 is moved leftwards in the figure against the
biasing force of the spring 13. Centrally of the piston 11 is
formed a chamber 17, into which is fed the hydraulic brake fluid
from the master cylinder. The chamber 17 and the left-hand space of
the piston 11 are normally in communication with each other through
the passage 29. In the passage 29 is disposed a check valve 7
constituted by a ball to prevent backward flowing of the hydraulic
brake fluid from the wheel cylinder 9 during control which will be
described later.
A control fluid such as air is delivered from a tank 19 by means of
a pump 21, then passes through a check valve 23 and is stored in an
accumulator 35.
When the internal pressure of the accumulator exceeds a
predetermined level, a switch 31 turns off to stop the supply of
electric power to a motor 33 and the operation of the pump 21
stops.
A hold valve 25 and a decay valve 27 are controlled by a control
section 37. The hold valve 25 is constituted by a normally closed
solenoid valve, while the decay valve 27 is constituted by a
normally open solenoid valve.
The control section 37 controls the opening and closing the hold
valve 25 and decay valve 27 which together function as a brake
pressure controller, whereby it is made possible to control
pressurizing, pressure holding and pressure reduction for the
hydraulic brake fluid in the wheel cylinder 9 through the pressure
accumulating device 5.
A distance sensor 39 is connected to the control section 37. As the
distance sensor 39 there is used a sensor which utilizes ultrasonic
wave, laser beam, image processing, or infrared ray.
The control section 37 uses a buzzer 41 or a lamp 43 for giving a
warning to the driver, using light or sound.
A steering sensor 49 has a function of judging whether a steering
operation is being performed or not.
The control made by the control section 37 will be described below
with reference to FIG. 1.
First, the distance X.sub.N from an obstacle, e.g. a front vehicle,
is determined by the distance sensor 39 of this car.
The distance X.sub.N is obtained at every operation cycle T, and a
relative velocity Vs with respect to the front vehicle is
determined from changes of X.sub.N with time (step 101). Judgment
is made as to whether the value of the relative velocity Vs is
positive or negative for judging whether this vehicle is
approaching the front vehicle (step 113).
If it is judged in step 113 that this vehicle is approaching the
front vehicle, there is calculated an estimated time Tx which will
be taken until contact, or rear-end collision, with the front
wheel, from both the relative velocity Vs and the distance X.sub.N
(step 102).
If Tx is smaller than a predetermined value T.sub.0 (step 103) and
also smaller than T.sub.1 (T.sub.1 <T.sub.0) (step 104), the
hold valve 25 is opened and the decay valve 27 is closed, thereby
allowing the control fluid in the accumulator 35 to be fed into the
port 15 of the pressure accumulating device 5.
As a result, the piston 11 moves leftwards in the figure, whereby
the hydraulic brake fluid in the pressure accumulating device 5 is
fed into the wheel cylinder 9 to pressurize the cylinder, thus
effecting a braking operation (step 105). At the same time, stop
lamps 44 provided in rear positions of the vehicle come on (step
112).
When in step 103 the estimated time Tx is longer than the reference
time T.sub.1 (step 104) though it is shorter than the reference
time T.sub.0 (step 103), a judgment is made as to whether the brake
pedal 1 has been depressed or not (step 106). If the brake pedal
has not been depressed, the lamp 43 will blink and the buzzer 41
will sound, thus issuing a warning (step 107). At the same time,
the hold valve 25 opens and the decay valve 27 closes for only a
predetermined time. As a result, the piston 11 moves only a
predetermined distance leftwards in the figure to deliver only a
predetermined amount of the hydraulic brake fluid to the wheel
cylinder 9 to pre-pressurize the cylinder (step 108).
The said pre-pressurizing is performed until the fluid pressure in
the wheel cylinder 9 becomes about 5 kgf/cm.sup.2 so as to cause a
light drag state of the brake as shown in FIG. 2. In the initial
stage of pressurizing, as shown in the same figure, the increase of
fluid pressure is small for the amount of fluid fed due to a brake
shoe gap or the loss of the hydraulic brake fluid. Therefore, if a
small amount of the hydraulic brake fluid is fed beforehand by such
pre- pressurizing, it is possible to generate a sufficiently high
fluid pressure at a small amount of the fluid in the subsequent
main pressurizing operation, thereby permitting an improvement in
the response characteristic of braking.
If the brake pedal has been depressed in step 106, the warning is
cancelled (step 109), then the hold valve 25 is closed and the
decay valve 27 opens for delivery of the control fluid from the
port 15, so that the piston 11 moves rightwards in the figure under
the action of the spring 13 and the pre-pressurizing is released
(step 110).
Braking is performed by a leftward movement in the figure of the
piston 11 (step 105) or by depression of the brake pedal 1, and if
as a result the distance Tx is larger than T.sub.0 (step 103), the
warning is cancelled, the hold valve 25 closes and the decay valve
27 opens, allowing the control fluid to be discharged from the port
15, so that the piston 11 moves rightwards in the figure under the
action of the spring 13 and the pre-pressurizing and main
pressurizing are released (step 111).
At this time, once the piston 11 returns to the rightmost end, the
check valve 7 opens to open the passage 29.
Embodiment 2
FIG. 4 shows an automatic brake control according to another
embodiment of the present invention.
The flow of control made by the control section 37 in this
embodiment 2 is different from that of the above embodiment 1 in
that processings A and B which are enclosed with broken lines are
added.
More specifically, a relative velocity Vs with respect to a front
vehicle is calculated from changes of the vehicle-to-vehicle
distance X with time (step 101), and if it is judged that this
vehicle is approaching the front vehicle (step 113), an estimated
time Tx until collision is calculated from both Vs and X (step
102), and after comparing the estimated time with a predetermined
value T.sub.0 (step 103), a relative acceleration V's is calculated
from the relative velocity Vs, then judgment is made as to whether
the value of the relative acceleration V's is positive or negative
(step 401) and if it is positive, that is, if the speed is high, Vs
and Tx are multiplied together and judgment is made as to whether a
relative velocity Vs.sub.2 : (Vs+V's.multidot.Tx) is positive or
negative at the time when the rear-end collision estimated time Tx
has elapsed (step 402). If it is negative, the flow shifts to step
111 to cancel the warning and release the pressure.
According to such flow in processing B, even a relative velocity at
the elapsed time point of the rear-end collision estimated time is
judged, whereby unnecessary warning and application of pressure are
avoided and hence any extra burden is imposed on the driver.
In the processing B, not only whether the brake pedal 1 has been
depressed or not is judged, but also whether a steering operation
is being performed or not is judged from a signal of a steering
sensor 49 as shown in FIG. 3 (step 403). If the answer is
affirmative, it is judged that the driver has the intention of
avoiding collision, and the warning is cancelled and the
application of pressure released (step 404).
On the other hand, when the brake pedal 1 is not depressed nor is
performed a steering operation, a warning is issued (step 405). At
this time, there may be conducted such pre-pressurizing (step 108
in FIG. 1) as described above in the embodiment 1.
According to the automatic brake control system of the present
invention, as set forth in the above embodiments, a warning is
issued and braking is performed in accordance with whether the
estimated time Tx up to collision is larger or smaller than the
predetermined value T.sub.0 or T.sub.1. Therefore, braking can be
done in a state very close to the actual driving sense.
For example, consideration will now be given to two cases, in one
of which the running speed of this vehicle is 100 km/h and that of
a front vehicle is 50 km/h, and in the other, the running speed of
this vehicle is 100 km/h and that of a front vehicle is 0 km/h
(stopped). According to the prior art, since both cases are the
same in the running speed (100 km/h) of this vehicle, braking is
started when the vehicle-to-vehicle distance reaches a value
(assumed to be 50 m) which has been determined beforehand in
accordance with the running speed of this vehicle. In the former
case, braking is started at a time point of 3.60 seconds up to
collision, and in the latter case, braking is not started until
when the time up to collision is 1.80 second. Thus, as long as
judgment is made on the basis of the time up to collision, there is
a great unevenness in the time point at which braking is started.
This indicates a discrepancy from the actual driving sense.
On the other hand, according to the present invention, if a preset
value T.sub.1 of an estimated time up to collision in the former
case is 3.60 seconds (distance from the front vehicle: 50 m),
braking can be started when the estimated time Tx has become 3.6
seconds even in the latter case where the front vehicle is stopped,
that is, braking can be started at the time when the distance from
the front vehicle is 100 m (50 m in the prior art).
Also in actual driving, the driver drives his vehicle while
grasping the state of a front vehicle, and when the front vehicle
is braked suddenly or is stopped, the driver of this vehicle
applies the brake at a relatively long distance. According to the
present invention, a braking action can be exhibited in a state
close to such actual driving sense.
Even when the estimated time Tx up to collision is larger than
T.sub.1, if it is smaller than T.sub.0, a warning is issued to call
the driver's attention, thereby permitting a smooth braking
operation to be performed by the brake pedal 1.
Further, since pre-pressurizing (see FIG. 2) is conducted
simultaneously with the issuance of a warning, it is possible to
improve the response characteristic of actual braking. More
particularly, the time T.sub.1 may be set at an extremely short
time lest the automatic braking system should operate in a too
early stage, but in order to ensure braking in such a short time,
it is necessary to improve the response characteristic of the
system. Also when the driver applies the brake by depressing the
brake pedal 1 after the issuance of a warning, it is necessary to
perform a prompt braking operation because the estimated time Tx up
to collision is smaller than T.sub.0, and hence improving the
response characteristic of the system is advantageous.
Although in the above embodiments the obstacle is a front vehicle,
even when the obstacle is such a stationary structure as a
guardrail, the automatic brake control system of the present
invention is applicable effectively. In this case, like the case
where the front vehicle is stopped, braking is started at a fairly
longer distance from the obstacle than in the prior art, thus
ensuring safety.
According to the automatic brake control system of the present
invention, as set forth hereinabove, an estimated time Tx up to
contact with an obstacle such as a front vehicle is determined on
the basis of a relative velocity Vs which also takes into account
the moving speed of the obstacle, and braking is performed in
accordance with the estimated time Tx, so even when the running
speed of this vehicle is constant, braking is conducted if Tx is
small, even at a long distance X, thus permitting a braking
operation to be carried out in a state close to the actual driving
sense, whereby a safe braking method can be provided.
According to the present invention, moreover, even when braking is
performed using an automatic braking system, it is possible to call
the driver's attention in a succeeding vehicle because stop lamps
come on and hence possible to enhance the safety of running
vehicles.
* * * * *